Wann immer sich die Größe deines Fensters ändert erhältst du eine
WM_SIZE-Benachrichtigung, die dann im Parameter wParam Auskunft darüber gibt, was passiert ist.
Zitat:
SIZE_MAXHIDE
Message is sent to all pop-up windows when some other window is maximized.
SIZE_MAXIMIZED
The window has been maximized.
SIZE_MAXSHOW
Message is sent to all pop-up windows when some other window has been restored to its former size.
SIZE_MINIMIZED
The window has been minimized.
SIZE_RESTORED
The window has been resized, but neither the SIZE_MINIMIZED nor SIZE_MAXIMIZED value applies.
Die
VCL löst dann übrigens das Ereignis OnResize aus.